= Coding Methods

The following is a short set of guidelines to follow while programming. It does
not address coding styles, function naming methods, or debugging methods.
Rather, it describes the processes which should go on in the programmer’s mind
while they are programming.

Coding standards apply to function names, the look of the code, and coding
consistency. Coding methods apply to the daily practices used by the programmer
to write code.

== Comment your code

If you don’t, you’ll be forced to debug it six months later, when you have no clue
as to what it’s doing.

If someone _really_ hates you, you’ll be forced to debug un-commented code that
someone else wrote. You don’t want to do that.

For FreeRADIUS, use doxygen `@`-style comments so you get the
benefits of the developer documentation site, https://doc.freeradius.org/.

== Give things reasonable names

Variables and functions should have names. Calling them `x`, `xx`,
and `xxx` makes your life hell. Even `foo` and `i` are
problematic.

Avoid smurfs. Don’t reuse struct names in field names, i. e.

[source,c]
----
struct smurf {
  char *smurf_pappa_smurf;
}
----

If your code reads as full English sentences, you’re doing it right.

== Check input parameters in the functions you write

Your function _cannot_ do anything right if the user passed in garbage
and you were too lazy to check for garbage input.

`assert()` (`fr_assert()`) is ugly. Use it.

[NOTE]
====
GIGO, "Garbage In, Garbage Out," is wrong. If your function gets
garbage input, it should complain loudly and with great
descriptiveness.
====

== Write useful error messages

"Function failed" is useless as an error message. It makes debugging the code
impossible without source-level instrumentation.

If you’re going to instrument the code at source level for error messages, leave
the error messages there, so the next sucker won’t have to do the same work all
over again.

== Check error conditions from the functions you call

Your function _cannot_ do anything right if you called another function, and
they gave you garbage output.

One of the most common mistakes is:

[source,c]
----
fp = fopen(...);
fgetc(fp);       /* core dumps! */
----

If the programmer had bothered to check for a `NULL` fp (error
condition), then they could have produced a descriptive error message
instead of having the program core dump.

== Core dumps are for weenies

If your program core dumps accidentally, you’re a bad programmer. You don’t know
what your program is doing, or what it’s supposed to be doing when anything goes
wrong.

If it hits an `assert()` and calls `abort()`, you’re a genius. You’ve thought
ahead to what _might_ go wrong, and put in an assertion to ensure that it fails
in a _known manner_ when something _does_ go wrong. (As it usually does…)

== Initialize your variables

`memset()` (`talloc_zero()`) is your friend. `ptr = NULL` is nice,
too.

Having variables containing garbage values makes it easy for the code to do
garbage things. The contents of local variables are inputs to your function. See
xref:#_check_input_parameters_in_the_functions_you_write[#3].

It’s also nearly impossible for you to debug any problems, as you can’t tell the
variables with garbage values from the real ones.

== Don’t allow buffer over-runs

They’re usually accidental, but they cause core dumps. `strcpy()` and `strcat()`
are ugly. Use them under duress.

`sizeof()` is your friend.

== `const` is your friend

If you don’t mean to modify an input structure to your function, declare it
`const`. Declare string constants `const`. It can’t hurt, and it allows more
errors to be found at compile time.

Use `const` everywhere. Once you throw a few into your code, and have it save
you from stupid bugs, you’ll blindly throw in `const` everywhere. It’s a
life-saver.

== Use C compiler warnings

Turn on all of the C compiler warnings possible. You might have to turn some off
due to broken system header files, though. But the more warnings the merrier.

Getting error messages at compile time is much preferable to getting core dumps
at run time. See xref:#_initialize_your_variables[#7].

Notice that the C compiler error messages are helpful? You should write error
messages like this, too. See xref:#_write_useful_error_messages[#4].

== Avoid UNIXisms and ASCIIisms and visualisms

You don’t know under what system someone will try to run your code. Don’t demand
that others use the same OS or character set as you use.

Never assign numbers to pointers. If foo is a `char*`, and you want it to be be
`NULL`, assign `NULL`, not `0`. The zeroth location is perfectly as addressable
as any other on plenty of OSes. Not all the world runs on Unix (though it should
:) ).

Another common mistake is to assume that the zeroth character in the character
set is the string terminator. Instead of terminating a string with `0`, use
`'\0'`, which is always right. Similarly, `memset()` with the appropriate value:
`NULL`, `'\0'`, or `0` for pointers, chars, and numbers.

Don’t put tabs in string constants, either. Always use `'\t'` to represent a
tab, instead of ASCII 9. Literal tabs are presented to readers of your code as
arbitrary whitespace, and it’s easy to mess up.

== Make conditionals explicit

Though it’s legal to test `if (foo) {}` if you test against the appropriate
value (like `NULL` or `'\0'`), your code is prettier and easier for others to
read without having to eyeball your prototypes continuously to figure out what
you’re doing (especially if your variables aren’t well-named). See
xref:#_give_things_reasonable_names[#2].

== Test your code

Even Donald Knuth writes buggy code. You’ll never find all of the bugs in your
code. But writing a test program definitely helps.

This means that you’ll have to write your code so that it will be easily
testable. As a result, it will look better and be easier to debug.

== Hints, Tips, and Tricks

This section lists many of the common `rules` associated with code submitted to
the project. There are always exceptions… but you must have a really good reason
for doing so.

== Read the Documentation and follow the CodingStyle

The FreeRADIUS server has a common coding style. Use real tabs to indent. There
is whitespace in variable assignments (`i = 1`, not `i=1`).

When in doubt, format your code to look the same as code already in the server.
If your code deviates too much from the current style, it is likely to be
rejected without further review, and without comment.

== #ifdefs are ugly

Code cluttered with `#ifdef` s is difficult to read and maintain. Don’t do it.
Instead, put your `#ifdef` s in a header, and conditionally define `static
inline` functions, or macros, which are used in the code. Let the compiler
optimize away the 'no-op' case.

Simple example, of poor code:

[source,c]
----
#ifdef CONFIG_MY_FUNKINESS
  init_my_stuff(foo);
#endif
----

Cleaned-up example:

(in header):

[source,c]
----
#ifndef CONFIG_MY_FUNKINESS
  static inline void init_my_stuff(char *foo) {}
#endif
----

(in the code itself):

[source,c]
----
init_my_stuff(dev);
----

== `static inline` is better than a macro

Static inline functions are greatly preferred over macros. They provide type
safety, have no length limitations, no formatting limitations, and under gcc
they are as cheap as macros.

Macros should only be used for cases where a static inline is clearly suboptimal
(there a few, isolated cases of this in fast paths), or where it is impossible
to use a static inline function (such as string-izing).

`static inline` is preferred over `$$static __inline__$$`, `extern inline`, and
`$$extern __inline__$$`.

== Don’t over-design

Don’t try to anticipate nebulous future cases which may or may not be useful:
_Make it as simple as you can, and no simpler._

Split up functionality as much as possible. If your code needs to do two
unrelated things, write two functions. Mashing two kinds of work into one
function makes the server difficult to debug and maintain.

